The first billion people accumulated over a leisurely interval, from the origins of humans hundreds of thousands of years ago to the early 1800s.

Adding the second took another 120 or so years.

Then, in the last 50 years, humanity more than doubled,
surging from three billion in 1959
to four billion in 1974,
five billion in 1987
and six billion in 1998.
The world’s population will reach seven billion in 2012.

Can the Planet Support 10 Billion People?

How will countries feed and shelter populations that are expected to soar by century’s end?

— Ines Kuhn